In association with GIS technology, grid-distributed hydrological model is used to study the flood response caused by underlying surface change in the sub-basin of Baipenzhu reservoir in Dongjiang River basin. In light of the status quo of land use in this basin, 9 underlying surface scenarios are built by scenario analysis, and three typical floods respectively of large, medium, and small scale are chosen to quantitatively analyze the flood response caused by underlying surface change. It is found that forestry and its spatial distribution can effectively retain rainfall, reduce flood peak, and postpone flood peak lag time. In this sense, the protection of forestry, in particular, forestry along the river channel and in the upper reaches of the basin, is significant for the flood control and disaster mitigation in the basin. Moreover, since urbanization will increase runoff yield and speed up confluence, which is detrimental to flood control, hydropower projects are of great help by controlling floods in tributaries of the basin. Response of big floods caused by underlying surface change is greater than that of small floods.